As a conventional valve timing change apparatus to change the open-close timing of an intake valve or an exhaust valve of an internal combustion engine, the structure which changes the rotational phases of a cam shaft to drive the intake valve or the exhaust valve and a crank shaft is known. For example, such a structure is disclosed in Japanese Patent No. 3033582, Japanese Patent laid-open 2000-274215, etc.
The apparatus disclosed in Japanese Patent No. 3033582 comprises an advancing oil-pressure chamber and a retarding oil-pressure chamber disposed at both sides of a vane which rotates within a specific angle range in a housing, and a lubricating oil passage communicating with both oil-pressure chambers. Then, by a switching valve (namely, an oil control valve) disposed at some midpoint of the lubricating oil passage, the lubricating oil introduced to both chambers is appropriately controlled, and pressure difference between both chambers is relatively generated. In this manner, the rotational phases of the cam shaft and the crank shaft are changed.
Further, with the apparatus disclosed in Japanese Patent Laid-open 2000-274215, relative rotation is generated between a specific rotating member and a cam shaft by electromagnetically generated braking torque, and the rotational phases of the cam shaft and the crank shaft are changed via a gear mechanism, such as a worm gear, a hypoid gear, etc.
However, with the apparatus disclosed in Japanese Patent No. 3033582, since the switching valve disposed at some midpoint of the lubricating oil passage switches the flow of the lubricating oil and directly controls the charge and discharge of the lubricating oil, the driving force of a pump for supplying the lubricating oil is directly added as a load to the engine. Further, oil pressure drop is caused while passing though the lubricating oil passage. The drop of the oil pressure becomes significant, especially when this apparatus is disposed at both the intake side and the exhaust side (namely, two-apparatuses mounted), or when two apparatuses are respectively disposed at each cylinder head of both sides of a V-shaped engine (namely, four-apparatuses mounted). When the oil pressure drops as mentioned above, the change to desirable open-close timing cannot be reliably performed.
On the other hand, to prevent the oil pressure drop, the capacity of the pump for supplying lubricating oil has to be enlarged, which causes upsizing of an engine, increase of an engine load, etc.
With the apparatus disclosed in Japanese Patent Laid-open 2000-274215, problems such as impact noise of the teeth caused by backlash etc. of the gears, phase fluctuation caused by thrust play at the hypoid gear, etc. arise. Further, because it is a gear mechanism, the apparatus becomes mechanically complicated and upsized, which causes upsizing of an engine.
The present invention was devised in view of the problems of the related art. The object of the present invention is to provide a valve timing change apparatus which can reliably change the open-close timing at all drive modes of an engine, without being affected by lubricating oil supply capacity, circumstance conditions, etc., while achieving load reduction to the engine, structural simplification, downsizing, and so on.